The present invention relates to an improved torque wrench which is adapted to transmit the rotation of an input shaft to an output shaft by a ratchet wheel rotatable by the crank motion of an eccentric ring and by which bolts, nuts and the like can be fastened or loosened easily and rapidly in a limited space without the necessity of moving the main body of the wrench.
Conventional torque wrenches of this type comprise two sprocket wheels for an input shaft and an output shaft and an endless chain reeved around the sprocket wheels for transmitting the rotation of the input shaft to the output shaft. We have already provided such a torque wrench. The known devices nevertheless have the following drawbacks. The chain power transmission system involves difficulties in giving a high power transmission ratio or affording output at an altered transmission ratio because of various limitations. Additionally the chain is unable to transmit the torque reliably and efficiently because the elongation or play involved in the chain tends to become progressively pronounced. Further when the input member is driven as by a motor, the wrench is likely to stop its operation with the rear end of the main body forcibly pressed against an obstacle or wall by a reaction upon completion of a nut fastening operation. The main body is then difficult to release, and a serious trouble could result.